Single html file upload for Assets in Grid in Channel Form - ExpressionEngine

Single html file upload for Assets in Grid in Channel Form.phtml

// Warning: this requieres latest (at this moment unpublished) version of Assets 2.5.1 addon

// So, I had a need to disable File browser that Assets comes with in frontend, 
// and use simple file input in a Grid fieldtype
// Official docs are ok, but not complete for use in the Grid
// http://docs.pixelandtonic.com/assets/templating/channel_form.html#using-a-file-input

// Lets say your Grid fieldtype is called 'grid_field'
// and your Assets field is 'col_id_10' (you can check what ID is in DB [check grid table for that fieldtype])

<input type="file" name="grid_field[rows][new_row_0][col_id_10]" />
// Use _filedir for local storage as mention in the official docs, I'm using S3 here
<input type="hidden" name="grid_field[rows][new_row_0][col_id_10_source]" value="1"/>

// Full example of Channel form
{exp:channel:form
    channel="your_channel"
    entry_id="{segment_3}" //You need to have entry_id because you are always editing eixisting entry
    return="your_return_url"
    limit="1"
    dynamic="no"
}
    <!-- Grid field hidden to mantain existing rows -->
    <div class="hidden">{field:properties_docs}</div>
    
    <!-- There will be probably more fields in the Grid, if you need to add them put them the same way (pay attention to col_id_XY) -->
    <input type="text" class="form-control" id="grid_title" name="grid_field[rows][new_row_0][col_id_11]">
    
    <!-- Assets field -->
    <input type="file" name="grid_field[rows][new_row_0][col_id_10]" />
    {!-- Use _filedir for local storage as mention in the official docs, I'm using S3 here --}
    <input type="hidden" name="grid_field[rows][new_row_0][col_id_10_source]" value="1"/>                                    
    
   <button type="submit" class="btn btn-purple">Send</button>

{/exp:channel:form}